body{
  background-color: black;
}
#world{
  position: absolute;
  top: 50%;
  left: 50%;
  width: 650px;
  height: 600px;
  /*background-color: wheat;*/
  /*已知宽高↓*/
  /*margin-left: -50px;*/
  /*margin-top: -50px;*/
  font-size: 0;
  /*不知道宽高↓*/
  transform: translateX(-50%) translateY(-50%);
}
#world > div{
  display: inline-block;
  height: 50px;
  width: 50px;

}
.wall{
  background-image: url("../images/wall.png");
}
.ground{
  background-image: url("../images/ground.png");
}
.coin{
  background: url("../images/coin.png") no-repeat;
}
.pacman{
  background: url("../images/pacman.png") no-repeat;
}
.pacman.left{
  background: url("../images/pacman_left.png") no-repeat;
}
.pacman.up{
  background: url("../images/pacman_up.png") no-repeat;
}
.pacman.down{
  background: url("../images/pacman_down.png") no-repeat;
}











